Mr J. D. Dana on the Volcanoes of the Moon. 13 



the Institute at Paris, by M. Rozet, in which the moon is 

 shewn to have been a globe in complete fusion, which has 

 s]owly cooled ; and its peculiarities are dwelt upon as an 

 exhibition, in many respects, of the former state of our own 

 planet.* 



In all the geological observations which have been hither- 

 to made with regard to the moon, one important feature re- 

 mains unsatisfactorily explained. I refer to the vast magni- 

 tude of its craters. It is not surprising that, in view of their 

 stupendous size, many should have been incredulous as to 

 their crater character, and preferred to designate them by 

 some non-committal term, as circular ridges, or ring-moun- 

 tains ; nor that geologists, in general, have hardly ventured 

 to acknowledge their belief in these lunar wonders. Imagine, 

 if possible, in place of an ordinary crater, circular areas 50 

 to 150 miles in diameter, and 10,000 to 20,000 feet in depth. 

 Such are many of the lunar craters ; and they are crowded 

 in great numbers over the larger part of its surface, vary- 

 ing from even a more capacious magnitude, down to those 

 that measure but a few miles in breadth. It is not astonish- 

 ing that there should be found much difficulty in reconciling 

 their features with those of Vesuvius and Etna, hitherto re- 

 ceived too generally as the types of volcanoes and volcanic 

 action. The crater of Kilauea in the Hawaiian Islands is of 

 a wholly different character, and I propose to present some 

 illustrations which it affords, appealing to such general facts 

 regarding it as are already well known. If I mistake not, it 

 will be found to give a full interpretation of whatever has 

 been considered mysterious in these lunar ring-mountains. 

 After tliese illustrations, we may return again to earth, and 

 apply the knowledge which we have derived abroad, in ex- 

 emplifying the former geological history of our own planet. 



We may first consider the general features of the moon's 

 surface. 



About two-thirds of the lunar hemisphere in view, com- 

 prising almost the whole of the southern half and the north- 

 east quarter, are covered thickly with volcanic mountains. 



* Sur la S616nologie, by M. Uozet, Comptes Uendus, 1846, xxii., 470. 



